Schemers.org has a long list of interpreters (including compilers, even some that target popular virtual machines). Just follow the implementations link.
Here are some suggestions:
MIT Scheme (aka scm) comes from MIT, where the authors of The Wizard Book work. It’s available for Unix, MSDOS, and Mac OS (and a bunch of other platforms).
MIT Scheme has a nice emacs integration, though note that this integration doesn’t work on Windows because it requires unix signals for its operation. However, the Windows installer comes with Edwin IDE, which is very much like a stripped-down Emacs.
PLT Scheme (mzscheme and drscheme)—DRScheme offers a full IDE, has an integrated documentation system and other features for a beginner. It targets MS Windows, Unix, and Mac OS X.
Take a look at section 11.2, with the heading, “Contours,” in this page from the documentation Isn’t that a neat feature?
mzscheme is a plain terminal prompt version for PLT Scheme
This one caught my eye because its manual claims to be able to target the .Net CLR (with options for compiling with Mono as well) and the JVM.
The GNU project’s Scheme interpreter and extension language.